Retropleural Approach to the Ventral Thoracic and Thoracolumbar Spine

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Chapter 52 Retropleural Approach to the Ventral Thoracic and Thoracolumbar Spine

Two of the most widely used approaches to the ventral thoracic and thoracolumbar spine are the transpleural thoracotomy and the lateral extracavitary approach.^1,² Each approach has its advantages and disadvantages. The major advantage of the ventrolateral transpleural thoracotomy is that it provides unparalleled exposure of the ventral vertebral column over several segments. Nevertheless, this exposure has several disadvantages. First, this approach is characterized by an extensive incision and soft tissue dissection that are necessitated by a deep operative field. Second, because with this approach the chest cavity is entered from the ventrolateral chest quadrant, significant retraction of the unprotected lung is required. Finally, identification and decompression of the ventral spinal canal are also problematic, because the rib head partially obscures the spinal canal and the epidural veins are difficult to control via this trajectory. The aforementioned factors can create a less secure operative environment, increase surgical morbidity, and hinder the attainment of the surgical objective(s).

The lateral extracavitary approach is particularly useful when circumferential spinal exposure is needed, but it is impractical for isolated ventral vertebral column exposure. Ventral vertebral exposure with this technique requires an extensive and often bloody paraspinal muscle and foraminal dissection. Intercostal nerves are sacrificed to optimize exposure, which may result in a painful neuroma or abdominal wall muscle weakness at lower thoracic and thoracolumbar levels. The foraminal dissection may inadvertently occlude a medullary vessel, which may risk spinal cord infarction. Finally, despite the extensive dissection, direct ventral spinal canal visualization extends only to the midline and provides insufficient exposure to place a lateral spinal implant.

A retropleural thoracotomy, ideally, is more suited for a ventral exposure of the thoracic and thoracolumbar spine.³^–⁷ Similar to the situation in ventrolateral thoracotomy, the line of vision provided with a retropleural thoracotomy is ventral to the ventral aspect of the spinal canal, but because the chest cavity is entered more dorsally, there is a significantly shorter distance to the ventral vertebral column and canal. The extrapleural nature of the dissection allows safer and more secure lung retraction and avoids postoperative tube thoracostomy placement. This approach allows for earlier identification and entry into the lateral spinal canal, via a resected pedicle. It greatly facilitates ventral spinal canal decompression through the disc space and vertebral bodies. Unlike the lateral extracavitary approach, however, mobilization or sacrifice of the foraminal neurovascular structures is avoided. Thus, retropleural thoracotomy represents a hybrid surgical approach, incorporating the advantages of both standard transpleural ventrolateral and dorsolateral extrapleural approaches while avoiding their limitations.

Operative Planning

Retropleural thoracotomy is an appropriate approach for localized ventral thoracic and thoracolumbar vertebral lesions between T3 and L2. The side of the operative approach is determined primarily by the location of the lesion. Eccentric lesions are approached ipsilaterally. The choice of the approach for central lesions is determined by the proximity of the great vessels and viscera. For high thoracic lesions, the aortic loop favors a right-sided approach. Either side is appropriate at midthoracic levels, although an ectatic aorta in older patients may obscure the field with a left-sided approach. At the thoracic and thoracolumbar levels, a left-sided approach is preferred to avoid the vena cava and retraction of the liver.

Consistency must be ensured between the methods of preoperative and intraoperative determination of pathologic level to avoid a discrepancy. This discrepancy is particularly likely to occur when the preoperative levels are determined by MRI. MRI identifies levels according to an end-vertebrae reference point. For a lower thoracic lesion, for example, the pathologic level is numbered by counting up from the sacrum. This creates two areas of uncertainty. First, there may be transitional lumbosacral vertebrae. Second, MRI does not identify the number of ribs, size of the end rib, and number of nonrib lumbar vertebrae. From a surgical perspective, intraoperative localization is usually performed according to a surgically verifiable landmark, such as the end rib. Therefore, these two study methods must be consistent before surgery. If the location of the pathology has been identified with MRI, plain radiographs should be obtained to determine the size of the end rib and the number of nonribbed lumbar vertebrae.

Surgical Technique

After appropriate arterial and venous line access has been established, induction and intubation are performed. A double-lumen tube is used for lesions above the T6 vertebral level. An epidural catheter may be placed after intubation or at the conclusion of the procedure for postoperative pain management. A broad-spectrum antibiotic is usually administered 30 minutes before the skin incision, and this may be continued for two postoperative doses. The patient is carefully turned into a lateral position on a beanbag chair, with a small, soft roll under the dependent axilla. The upper arm is supported on a pillow or sling. The lower leg is slightly flexed at the hip and knee to help secure the position. All bony prominences and subcutaneously coursing nerve trunks must be well padded. The ulnar nerve at the elbow and the peroneal nerve at the fibular neck are particularly vulnerable areas. Thoracolumbar lesions should be centered over the kidney break. The skin incision is planned according to the level of exposure. For midthoracic lesions (T5-9), a 14-cm skin incision should extend from a point 4 cm off the dorsal midline to the dorsal axillary line. Extension of the incision toward the midaxillary line expands ventral access and may be required in some cases (Fig. 52-1, center incision). A curved incision that parallels the medial and inferior scapular border is used for upper (T3-4) thoracic lesions (see Fig. 52-1, right incision). For thoracolumbar exposure (T10-L2), the incision should parallel the rib one spinal segment above the pathologic level because of the more caudal inclination of the proximal portion of the lowest ribs (see Fig. 52-1, left incision). Therefore, whereas the approach to a T7-8 disc is exposed through the T8 rib bed, a T12 lesion is approached through the bed of the T11 rib.

FIGURE 52-1 Patient positioning and skin incisions for retropleural thoracotomy.

The skin incision is carried down to the rib (Fig. 52-2). A 10- to 12-cm rib segment, extending from the costotransverse ligament to the dorsal axillary line, is subperiosteally exposed and removed with rib shears (Fig. 52-3). The exposed bone surfaces are waxed. Note that the proximal 4 cm of the rib, extending from the costotransverse articulation to the rib head, has yet to be removed. The bed of the resected rib is now inspected. Muscle fibers of an inconstant subcostal muscle may be seen. At thoracic levels above T10, the endothoracic fascia will be identified in the rib bed. The endothoracic fascia is analogous to the transversalis fascia of the abdominal cavity.⁸ Both types of fascia line the walls of their respective visceral cavities and are reflected onto the surface of the diaphragm. The endothoracic fascia is tightly applied to or is continuous with the inner periosteum of the rib and vertebral bodies. The parietal pleura maintains its attachment to the chest wall through a surface tension seal with the inner surface of the endothoracic fascia. The intercostal vessels, nerves, and sympathetic chain are contained within the endothoracic fascia. Although only a potential (subendothoracic) space exists between the endothoracic fascia and the parietal pleura, a small amount of fluid and loose adipose tissue is occasionally identified, particularly dorsally near the rib head and vertebral bodies. Because the endothoracic fascia is continuous with the inner periosteum of the rib, it may be inadvertently torn during rib dissection and removal. This is common in older patients. If the endothoracic fascia is intact, it should be incised in line with the rib bed (Fig. 52-4). The underlying parietal pleura is bluntly and widely separated from the endothoracic fascia, either manually or with a Kittner (peanut) clamp (Fig. 52-5). The endothoracic fascia incision is continued dorsally to the margin of the cut surface of the remaining proximal rib. Blunt dissection of the pleura off the proximal rib head extends dorsally to expose the vertebral bodies and disc space. When the ventral convex border of the vertebral body has been exposed, a self-retaining, table-mounted retractor maintains exposure of the vertebral column (Fig. 52-6).

FIGURE 52-2 Skin incision is carried down to expose the rib to be resected.

FIGURE 52-3 After a careful subperiosteal dissection, a 10- to 12-cm rib segment is removed.

FIGURE 52-4 The endothoracic fascia is incised in line with the bed of the resected rib. Note that the underlying pleurae are bluntly freed from the undersurface of the endothoracic fascia with gloved fingers.

FIGURE 52-5 A, The pleurae are bluntly freed from the inner surface of the endothoracic fascia with a Kittner clamp. B, After a wide pleural dissection, the remaining endothoracic fascia overlying the remaining rib head and vertebral bodies is incised, and the rib head is removed.

FIGURE 52-6 The endothoracic fascia opening has been continued onto the lateral aspect of the vertebral bodies. It is reflected away from the disc. The intercostal vessels remain within the reflected tissue. The thoracic sympathetic chain has been divided, and the disc has been incised.

The endothoracic fascia incision is continued dorsally over the remaining proximal rib segment and onto the vertebral body with electrocautery. This divides the sympathetic chain that descends within the endothoracic fascia, just ventral to the rib head insertion on the surface of the vertebral column. The musculoligamentous attachments, including the costotransverse and stellate ligaments, are detached from the rib head segment, which is then removed. Removal of the rib head is critical because it allows identification of the pedicle (through which the lateral spinal canal entry will subsequently be accessed). For thoracic disc removal, the incised endothoracic fascia and vertebral body periosteum are elevated in either direction from the disc space to the midvertebral body. The intercostal vessels, which run transversely at the midvertebral level, are preserved within the reflected tissue. The margins of the pedicle are defined with angled curettes and nerve hooks. The pedicle is resected with a high-speed drill or Kerrison rongeurs. Removal of the pedicle provides lateral spinal canal identification and entrance. This lateral canal entrance, unlike the lateral extracavitary approach, avoids a bloody foraminal dissection as well as possible nerve root and radiculomedullary artery injury.

The lateral disc anulus fibrosus is sharply incised. The disc is evacuated with curettes and rongeurs. The adjacent end-plate and vertebral body margins are removed with a high-speed drill. The width and depth of the disc and adjacent vertebral body dissection must be adequate to ensure ventral spinal canal exposure and decompression. The depth should extend 3 to 3.5 cm from the lateral body vertebral margin to reach the contralateral pedicle. The width should extend about 1 cm on either side of the disc into the adjacent vertebral bodies (wider for larger calcified discs that have migrated, usually caudally, behind the vertebral body). The dissection is continued dorsally toward the spinal canal with disc curettage and a high-speed drill (Fig. 52-7). Spinal canal identification through the disc space and adjacent vertebral bodies is readily achieved because of the previously exposed lateral spinal canal entrance through the resected pedicle bed. When the dissection is carried back to the dorsal cortical margin and dorsal anulus fibrosus, a sharp, reverse-angle curette is passed through the lateral spinal canal entrance to displace these structures away from the spinal canal and into the bed of the resected disc and adjacent vertebral bodies. This maneuver may precipitate epidural bleeding that can be effectively managed with bipolar cautery forceps, introduced through the lateral spinal canal margin or with small pieces of Surgicel. As in the ventral cervical region, a thin dorsal layer of posterior longitudinal ligament (PLL) often remains after resection of the thicker ventral portion of the PLL (which is firmly attached to the dorsal disc anulus). Many calcified thoracic disc fragments are suspended within this thin dorsal PLL laver and are not located intradurally as often as the literature suggests. The ventral spinal canal should be probed with a microdissector and nerve hook for identification and delivery of these fragments that are suspended within this layer of ligament. The dura mater should be clearly identified before the decompression is considered complete. After adequate spinal canal decompression has been achieved, an interbody autologous rib graft is placed, although its efficacy after routine discectomy has as yet to be established (Fig. 52-8).